I have been using Bitcoin Wallet (Andreas Schildbach) for some months on my HTC Desire, no problems. Having version 2.18 installed however, all my outgoing transactions are 'greyed' and appear only in wallet UI, leaving no trace in a blockchain, some are staying for several days unsent.

Am I the only 'unlucky' one, or did anyone else experience the same problem?

Have you checked if the transaction was broadcasted even though it is not included in a block? You can check it on http://blockchain.info. Did you include a fee in the transactions? Does the software connect to peers (you can monitor them from the menu)?

Well, don't forget that regular bitcoin clients (which Bitcoin Wallet connects to as peers) check that a fee is included even to *relay* a transaction in some cases. For example, if your transaction has outputs smaller than 1 cent (0.01 BTC) or if inputs to the transaction are not all 6-confirmed, I seem to remember (I don't have the source code handy right now so the numbers may be wrong) that the client will check that at least 0.0001 BTC is included as a fee before relaying the transaction.

The regular client won't let you try to broadcast a transaction that it would not accept itself, but the Android Bitcoin Wallet doesn't make such (admittedly arbitrary) checks, that may explain why the transaction are not being broadcast.